Method for hydrostatic extrusion of tubes and billets

ABSTRACT

In the hydrostatic extrusion of tubes, a billet is provided which has a bore at its rear end in which is inserted a sleeve of harder material than the material of the billet, for example steel in a billet of aluminium or copper, and the billet is then extruded through a die opening around a mandrel. The sleeve is of greater thickness than the space between the mandrel and the wall of the die opening so that it stops or retards extrusion when the sleeve reaches the point of the die opening.

United States Patent Brunosson Apr. 15, 1975 [54] METHOD FOR HYDROSTATICEXTRUSION 3,751,957 8/1973 Nilsson 72/60 OF TUBES AND BILLETS 3,807,0324/1974 Nilsson 72/60 Inventor: Gunnar Brunosson, Vasteras,

Sweden Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed:Feb. 8, 1974 Appl. No.: 440,874

Assignee:

Foreign Application Priority Data Mar. 7, 1973 Sweden 7303176 US. Cl72/60; 29/1875 Int. Cl B2ld 23/04 Field of Search 72/60, 253, 257, 258;

References Cited UNITED STATES PATENTS 8/1973 Stromblad 72/60 FOREIGNPATENTS OR APPLICATIONS 1,058,854 2/1967 United Kingdom 72/60 PrimaryExaminerRichard J. l-Ierbst [57] ABSTRACT 10 Claims, 8 Drawing FiguresMETHOD FOR HYDROSTATIC EXTRUSION OF TUBES AND BILLETS BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to amethod for manufacturing tubes by hydrostatic extrusion and to a billetintended to be used in the application of such method.

2. The Prior Art In hydrostatic extrusion of tubes, a tubular billet isinserted into a pressure chamber and is pressed out through a gapbetween a die opening and a mandrel under the effect of a surroundingpressure medium. The pressure level is high, usually between and kbar.It is therefore necessary to prevent the billet from being completelypressed out, since exposing a die opening involves an explosion-likeoutflow of the pressure medium, which may cause damage to the die, themandrel and the finished product and which may involve danger topersonnel. At the same time it is desirable that the material in thebillet should be utilized to the greatest possible extent, which meansthat the extrusion should be terminated as late as possible.

One purpose of the invention is to make it possible to terminate theextrusion at a very late stage so that the left-over billet is slight.Another purpose of the invention is to cut off a press product inconnection with the completion of the extrusion.

SUMMARY OF THE INVENTION According to the invention, an annular sleeveof a material which is harder than the material of the billet is appliedat its rear part. The sleeve is suitably pressed into the billet. A boreis formed in the billet having a diameter insignificantly smaller thanthe outer diameter of the sleeve. The sleeve has a larger inner diameterthan the mandrel which passes through the billet, thus securing aconnection between the gap between the billet and the mandrel and thespace in the pressure chamber outside the billet. The thickness of thematerial of the sleeve should be larger than the width ofthe gap betweenthe mandrel and the die. When the part of the billet where the sleeve islocated reaches the opening between the die and the mandrel, theextrusion conditions are affected so that the position of the billet canbe indicated. What happens when the sleeve reaches the die depends onits shape. If the sleeve has such a thickness of material at its frontpart that it is deformed so that it surrounds the mandrel in a sealingmanner, the pressure in the pressure chamber will rise since thematerial of the sleeve is harder than the material of the billet andtherefore requires a higher extrusion pressure at a certain extrusionratio than the material of the billet. The pressure increase can beindicated and used to generate a control signal which interrupts thesupply of pressure medium to the pressure generating punch of thepressure chamber. The sleeve may be formed so that it also cuts off anextruded tube when it reaches the die. However, if the thickness of thesleeve is such that it is not pressed into sealing contact with themandrel and if it has such an inner diameter that there is a thin gapbetween the mandrel and the sleeve when the sleeve reaches the die, thesleeve can cut off the extruded tube and the pressure medium will pressthe cut tube out of the die. When the size and length of the gap issuitable, the outflow of pressure medium can be limited to a harmlessspeed and magnitude. The outflow of the pressure medium or the pressingout of the tube can be indicated and a suitable control signal can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described moreclosely with reference to the accompanying figures. FIG. 1 showsschematically a pressure chamber with extrusion tools and an insertedbillet just after the start of extrusion; FIGS. 2-6 show variousembodiments of the sleeve and the location of these in the billet andFIG. 7 and 8 a die with residual billet after completed extrusion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the figures, 1 designates apart of a stand of an extrusion press, the rest of which is not shown.In the press there is a high pressure cylinder 2 which forms a pressurechamber 5 together with a pressure generating punch 3, projecting intothe cylinder, and a die 4. Between the cylinder 2 and the punch 3 andthe die 4, respectively, there are seals 6 and 7, respectively. In thepressure chamber 5 there are inserted a spacing collar 8 and a plate 9having holes 9' therein. A mandrel 10 which is attached to the plate 9forms a gap with the opening 11 in the die 4. Under the effect of apressure medium in the chamber 5 surrounding the billet 12, the billetis pressed out through the gap between the mandrel l0 and the opening 11in the die, thus forming a tube 13. At the rear part of the billet 12,which has a hole therethrough somewhat larger than the mandrel, there isinserted a sleeve 14 of a material which is harder than the material ofthe billet to be extruded.

As shown in FIGS. 2 and 3 a sleeve 14 having relatively thin walls isapplied at the rear end of the billet. The wall thickness of the sleeveshould exceed the width of the gap between the mandrel 10 and the wallin the die opening 11 in order that the sleeve may be able to stop theextrusion. The sleeve 14 has the same inner diameter as the hole in thebillet l2, and thus a somewhat larger diameter than the mandrel 10. Itis pressed into a bore 15 or 16, respectively. In the embodimentaccording to FIG. 2 the bore and the sleeve have the same length,whereas in the embodiment according to FIG. 3 the bore is longer thanthe sleeve. In the embodiment according to FIGS. 4 and 5, a sleeve 17having thick walls is positioned in a bore 18 or 19, respectively, inthe billet 12. In the embodiment according to FIG. 4 the bore and thesleeve have the same length, whereas in the embodiment according to FIG.5 the bore is longer than the sleeve. In the embodiment according toFIG. 6 an outwardly conical sleeve 20 is applied in a corresponding wayin a bore 21, the sleeve then having a larger diameter at its rear endthan at its front end.

FIG. 7 shows how, at the end of the extrusion, when the sleeve 14 hasmoved down to the die 4, the front end of the sleeve makes contact withthe die, the sleeve thus cutting off the tube at the die opening. Inthis case, the thickness of the sleeve wall is such that it iscompressed and makes contact with the mandrel in a sealing manner. Thecross-section of the sleeve should be so large in relation to thecross-section of the annular opening 11 between the die 4 and themandrel 10 that the ratio is greater than the possible extrusion ratiowith the pressure with which the material in the billet 12 can bepressed into the said gap. The pressing out the sleeve then requires ahigher pressure, and a pressure increase caused by the sleeve can beindicated and give rise to a control signal which interrupts the supplyof energy to the driving cylinder of the pressure generating punch.

H6. 8 shows how a sleeve with great wall thickness makes contact at theend of the extrusion with the die with its front end. The sleeve has cutoff the tube 13. The sleeve has such a strength that it is not deformedinto making contact with the mandrel 10, but an annular gap 22 remains.When the gap is small and the length of the gap relatively small thepressure drop during the flow of pressure medium from the pressurechamber and the out-flowing amount of pressure medium will be small. Thepressure medium flowing out through the gap 22 presses the last part ofthe tube 13 out of the die.

The billet may be, for example, of aluminum or copper and the sleeve ofsteel.

I claim:

1. A method for the hydrostatic extrusion of tubes which comprisesinserting into a pressure chamber having a die opening and a mandrelpassing through the die opening and of less diameter than the dieopening a billet having a central hole therethrough and having a bore atthe rear end, and a sleeve in said bore formed of a material which isharder than the material of the billet and has a larger inner diameterthan the diameter of the mandrel, the sleeve having a greater thicknessof material than the space between the die opening and the mandrel andbeing substantially shorter than the billet, thereby to prevent thebillet from being completely pressed out of the die opening.

2. A method as claimed in claim 1, in which the sleeve has substantiallythe same inner diameter as the inner diameter of the hole in the billet.

3. A method as claimed in claim 2, in which the bore is longer than thesleeve.

4. A method as claimed in claim 1, in which the sleeve has a greaterthickness of material at its rear end than at its front end.

5. A billet for use in the hydrostatic extrusion of tubes, having acentral bore therethrough and having a sleeve inserted in its rear endconcentric with the bore and of harder material than the material of thebillet and substantially shorter than the billet.

6. A billet as claimed in claim 5, in which billet has a bore at itsrear end with a larger diameter than the hole in the billet, the sleevebeing inserted in such bore.

7. A billet as claimed in claim 6, in which the bore is longer than thesleeve.

8. A billet as claimed in claim 5 in which the sleeve has a largerdiameter at its rear end than at its front end.

9. A billet as claimed in claim 5, in which the billet is of copper andthe sleeve is of steel.

10. A billet as claimed in claim 5, in which the billet is of aluminiumand the sleeve is of steel.

1. A method for the hydrostatic extrusion of tubes which comprisesinserting into a pressure chamber having a die opening and a mandrelpassing through the die opening and of less diameter than the dieopening a billet having a central hole therethrough and having a bore atthe rear end, and a sleeve in said bore formed of a material which isharder than the material of the billet and has a larger inner diameterthan the diameter of the mandrel, the sleeve having a greater thicknessof material than the space between the die opening and the mandrel andbeing substantially shorter than the billet, thereby to prevent thebillet from being completely pressed out of the die opening.
 2. A methodas claimed in claim 1, in which the sleeve has substantially the sameinner diameter as the inner diameter of the hole in the billet.
 3. Amethod as claimed in claim 2, in which the bore is longer than thesleeve.
 4. A method as claimed in claim 1, in which the sleeve has agreater thickness of material at its rear end than at its front end. 5.A billet for use in the hydrostatic extrusion of tubes, having a centralbore therethrough and having a sleeve inserted in its rear endconcentric with the bore and of harder material than the material of thebillet and substantially shorter than the billet.
 6. A billet as claimedin claim 5, in which billet has a bore at its rear end with a largerdiameter than the hole in the billet, the sleeve being inserted in suchbore.
 7. A billet as claimed in claim 6, in which the bore is longerthan the sleeve.
 8. A billet as claimed in claim 5 in which the sleevehas a larger diameter at its rear end than at its front end.
 9. A billetas claimed in claim 5, in which the billet is of copper and the sleeveis of steel.
 10. A billet as claimed in claim 5, in which the billet isof aluminium and the sleeve is of steel.